1. Field of the Invention
The invention involves a process to make ultrahigh contrast negative images by using photosensitive recording materials with silver halide emulsions, and a means for performing the process.
2. Description of the Related Art
In reprography, continuous tone images must frequently be converted to halftone images. Silver halide materials are used for this purpose and are developed by special processes to an ultrahigh contrast, that is, to a maximum slope in the density curve of more than 10. Known examples are lithographic processes with low sulfite hydroquinone developers containing formaldehyde, developing with hydroquinone and a superadditive auxiliary developer in the presence of hydrazine compounds, or developing at relatively high pH in the presence of development inhibitors, such as tetrazole compounds.
Certain amino compounds are often used in these processes to further increase contrast. EP-00 32 456-B1 claims a method for processing a recording material, in the presence of a hydrazine compound, with a hydroquinone/3-pyrazolidinone developer containing an amino compound in a quantity to increase contrast.
EP-04 73 342-A1 describes a photographic silver halide material that can be developed to ultrahigh contrast in a developer with a pH&lt;11. The photosensitive layer of this material contains a certain hydrazine compound and an amino or quaternary onium compound and is adjusted to a pH of at least 5.9.
Cationic surfactants and dyes with quaternary ammonium groups have long been known as development accelerators (L. F. A. Mason, "Photographic Processing Chemistry", London and New York, 1966, page 41 ff). U.S. Pat. No. 4,135,931 describes the use of certain pyridinium compounds to accelerate lithographic development. However, contrast is not increased in these known uses.
Developers containing an amino compound to increase contrast have disadvantages. The required concentration of the amino compound is considerable and is often close to the solubility limit. The solubility limit can be easily exceeded as a result of a temperature increase or slight concentration changes from water evaporation during use, and the amino compound is liberated. This results in irregular development and contaminates the recording material and the developing machine. Because of their vapor volatility, the liberated amino compounds also reach other parts of the development machine and cause unwanted contamination and corrosion.
A very unpleasant odor occurs in the use of developers containing known amino compounds, due to the high required concentration and volatility of these compounds.
Because the amino compounds have limited solubility, it is difficult to formulate the usual commercial developer concentrates. EP-A-02 03 521 discloses that salts of certain sulfonic acids and carboxylic acids can be used as solubilizing agents. However, the other problems cited are not solved by such additives.
Known developers usually have a pH above 11. Therefore, they are not adequately stable in use, and they corrode parts of the development machine.